The V. necatrix BM can infect nearly all tissues of silkworm (Fig. 1B), but the ovary and testis. No V. necatrix BM spore has been found in silkworm eggs, that is the V. necatrix BM has not been found that can be vertically transmitted to next generation of silkworm [2]. This is quite different to Nosema bombycis which can be vertically transmitted.